Title

Author

Date of Award:

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Advisor/Chair:

Carl A. Ernstrom

Abstract

The Harland-Ashworth test for measuring undenatured whey protein nitrogen in nonfat dry milk was modified to measure undenatured whey protein nitrogen in dried whey. The new test was designed to measure absorbance in Harland-Ashworth filtrates at 280 nm to eliminate difficulties associated with turbidimetric measurements. One gram dried whey was reconstituted in 25 ml pH 6.7 phosphate buffer (.lM) in a 25 x 150 mm test tube. Ten grams sodium chloride were added. The test tubes were incubated for 30 min in a water bath at 37C and shaken 8-10 times in the first 15 min. The tubes were removed from the water bath and cooled to room temperature. The contents of the tubes were filtered through S & S 602 filter paper. One milliliter of filtrate was diluted with 10 ml H2o and the total absorbance was measured against a blank of 1 ml phosphate buffer saturated with sodium chloride, then diluted with 10 ml H2o. One milliliter of filtrate was mixed with 10 ml 13.2% trichloroacetic acid and filtered through Whatman 42 filter paper. The nonprotein absorbance was measured against a blank containing 1 ml phosphate buffer saturated with sodium chloride, then mixed with 10 ml 13.2% trichloracetic acid and filtered through Whatman 42 filter paper. Undenatured whey protein absorbance was the difference between total absorbance and nonprotein absorbance. Undenatured whey protein nitrogen per gram dried whey equaled the undenatured whey protein nitrogen absorbance multipled by 50.5462 (R2 = 0.9743).

The test produced highly reproducible results with nonfat dry milk as well as dried whey. The relationship between absorbance and undenatured whey protein nitrogen was highly correlated and not solids concentration during heating or pH of the whey during heating.